Application of Tracer-Injection Techniques 

to Demonstrate Surface-Water and 

Ground-Water Interactions Between an 

Alpine Stream and the North Star Mine, 

Upper Animas River Watershed, 

Southwestern Colorado

By Winfield G. Wright and Bryan Moore

Prepared in cooperation with

Animas River Stakeholders Group and

San Juan County, Colorado

Water-Resources Investigations Report 03–4172

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

Gale A. Norton, Secretary

U.S. Geological Survey

Charles G. Groat, Director

U.S. Geological Survey, Reston, Virginia: 2003

For sale by U.S. Geological Survey, Information Services

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Denver, CO 80225

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Contents

Abstract..........................................................................................................................................1

Introduction...................................................................................................................................1

Description of Study Area..................................................................................................2

Purpose and Scope.............................................................................................................4

Previous Studies..................................................................................................................4

Water-Quality Sampling............................................................................................4

Surface Geophysics...................................................................................................5

Methods of Study..........................................................................................................................6

Tracer-Injection Methods..................................................................................................7

Continuous-Injection Tests.......................................................................................7

Slug-Injection Test......................................................................................................7

Sample Collection................................................................................................................7

Discharge Determinations.................................................................................................9

Interpretation of Tracer-Injection Data.................................................................10

Results of Tracer Recovery and Discharge Measurements................................................11

Tracer Recovery at the North Star Mine.......................................................................11

Continuous-Injection Tests.....................................................................................11

Slug-Injection Test...................................................................................................13

Tracer Recovery at Other Sites.......................................................................................14

Discharge of Springs, Streams, and Mine Outflows...................................................15

Surface-Water and Ground-Water Interactions at the North Star Mine..........................18

Summary......................................................................................................................................20

References Cited........................................................................................................................21

Appendix—Supplemental Information....................................................................................25

Laboratory Analytical Methods.......................................................................................25

Instrument Calibrations...........................................................................................25

Quality Assurance....................................................................................................27

Figures

1. Map showing location of the North Star Mine, Belcher Gulch, and other 

 historical mines in the area, upper Animas River watershed, 

southwestern Colorado..............................................................................................2

2. Map showing underground tunnels associated with the North Star, 

Sultan, and Gladstone Mines, tracer-injection points, and sampling 

sites in the vicinity of Belcher Gulch........................................................................3

3. Graph showing discharge, pH values, and dissolved-zinc concentrations in 

water from the North Star Mine, December 1997 through 

 October 1998.................................................................................................................5

4. Aerial photograph showing surface geophysical traverse done in Belcher

 Gulch by Ackman and others (1998).........................................................................6

iii
 5. Photographs showing tracer-injection test locations in Belcher Gulch......................................8

6. Photographs showing the high-altitude northern branch (site A) and southern

 branch (site B) of Belcher Gulch.....................................................................................................9

7–14. Graphs showing:

 7. Hypothetical example of tracer-recovery curve showing breakthrough, peak 

 concentration, and receding concentrations of tracer constituent......................................10

 8. Dissolved-lithium and dissolved-bromide concentrations in water from the North 

 Star Mine after injection began at site E....................................................................................12

 9. Optical brightener dye concentrations in water from the North Star Mine after 

 injection began at site G...............................................................................................................13

 10. Dissolved-sodium and dissolved-chloride concentrations in water from the 

 North Star Mine after injection began at site H.......................................................................14

 11. Dissolved-sodium concentrations in water from the North Star Mine after 

 injection began at site B...............................................................................................................15

 12. Dissolved-lithium and dissolved-sodium concentrations in water from the 

 Pittsburgh Mine..............................................................................................................................16

 13. Dissolved-lithium and dissolved-sodium concentrations in water from the 

 Sultan Mine.....................................................................................................................................17

 14. Dissolved-sodium concentrations in water from the spring in the Belcher

 Gulch alluvial fan............................................................................................................................18

 15. Schematic cross section of surface-water and ground-water interactions 

 between Belcher Gulch and the North Star Mine....................................................................20

 Appendix figures

A1. Graphs showing calibration curves for determination of dissolved lithium and 

 dissolved sodium by atomic absorption spectroscopy and optical 

 brightener dye by fluorometry........................................................................................................26

A2. Graphs showing calibration curves for determination of dissolved potassium

 by atomic absorption spectroscopy and dissolved bromide and 

 dissolved chloride by ion-selective electrode.............................................................................28

Tables

1. Discharge measurements of water from springs, streams, and mine 

 outflows.............................................................................................................................................19

 A1. Laboratory quality-assurance data..................................................................................................29

iv
Conversion Factors 

Multiply By To obtain

meter (m) 0.3048 foot (ft)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

mile (mi) 1.609 kilometer (km)

gallon (gal) 3.785 liter (L)

kilogram (kg) 0.454 pound (lb)

Abbreviated units used in this report

g gram

mL milliliter

mA milliamp

mV millivolt

nm nanometer

μm micrometer

mg/L milligram per liter

mL/min milliliter per minute

Acronyms used in this report:

AMLI U.S. Geological Survey Abandoned Mine Lands Initiative

ARSG Animas River Stakeholders Group

BLM Bureau of Land Management

USGS U.S. Geological Survey

v

Application of Tracer-Injection Techniques to Demonstrate 

Surface-Water and Ground-Water Interactions Between 

an Alpine Stream and the North Star Mine, Upper Animas 

River Watershed, Southwestern Colorado

Abstract

Tracer-injection studies were done in Belcher Gulch in 

the upper Animas River watershed, southwestern 

Colorado, to determine whether the alpine stream infiltrates 

into underground mine workings of the North Star Mine and 

other nearby mines in the area. The tracer-injection studies 

were designed to determine if and where along Belcher Gulch 

the stream infiltrates into the mine. Four separate tracer-injection tests were done using lithium bromide (LiBr), optical 

brightener dye, and sodium chloride (NaCl) as tracer solutions. Two of the tracers (LiBr and dye) were injected continuously for 24 hours, one of the NaCl tracers was injected 

continuously for 12 hours, and one of the NaCl tracers was 

injected over a period of 1 hour. Concentration increases of 

tracer constituents were detected in water discharging from the 

North Star Mine, substantiating a surface-water and groundwater connection between Belcher Gulch and the North Star 

Mine. Different timing and magnitude of tracer breakthroughs 

indicated multiple flow paths with different residence times 

from the stream to the mine. The Pittsburgh and Sultan Mines 

were thought to physically connect to the North Star Mine, but 

tracer breakthroughs were inconclusive in water from these 

mines. From the tracer-injection tests and synoptic measurements of streamflow discharge, a conceptual model was developed for surface-water and ground-water interactions between 

Belcher Gulch and the North Star Mine. This information, 

combined with previous surface geophysical surveys indicating the presence of subsurface voids, may assist with decisionmaking process for preventing infiltration and for the remediation of mine drainage from these mines. 

 Introduction

More than 3,000 historical mine features are scattered 

throughout the upper Animas River watershed in southwestern 

Colorado (C.L. Rich, U.S. Geological Survey, written commun., 2001). The historical mine features include prospect 

pits, mine entrances, shafts, waste rock piles, mill sites, and 

ore bins. There are more than 300 historical hardrock mines 

(C.L. Rich, U.S. Geological Survey, written commun., 2001), 

and these historical mine sites can affect water quality in 

the watershed (Simon and others, 2001). Some of the mines 

have extensive underground workings and many have water 

discharging from the mine tunnels (or mine entrances). There 

also can be high concentrations of trace elements in mine 

drainage that can result in substantial trace-element loads 

(discharge multiplied by the trace-element concentration). 

Through a process of ranking mines for cleanup, the Animas 

River Stakeholders Group (ARSG) prioritized mines in the 

watershed with the largest trace-element loads (Simon and 

others, 2001). Cleanup and remediation of these mines are 

intended to improve water quality in the upper Animas River 

watershed. Achieving cleanup of trace-element-rich mine 

drainage is a complex task, however, and the remediation 

methods typically involve active or passive treatment of the 

mine drainage through expensive and maintenance-intensive 

water-treatment systems. One alternative for mine-drainage 

cleanup is to prevent clean surface water from infiltrating into 

the mine before the water becomes contaminated. 

Mine tunnels frequently intersect fractures in bedrock 

that contain water. Water entering the mines can react with air 

and freshly exposed, deposit-related minerals, which increases 

the dissolved trace-element concentrations in water draining 

from the mines. Reactions between water and deposit-related 

minerals often lower pH, which results in acid mine drainage. 

Frequently, ground water infiltrating into the mine may have 

traveled a circuitous path from the land surface to the waterbearing fractures in the mine. In some cases, however, streams 

may infiltrate directly into mines, potentially contributing to 

acid mine drainage. In these cases, mine drainage may be prevented by diverting the stream or by sealing fractures beneath 

the stream that convey the water. This remediation method is 

called infiltration control. 

The North Star Mine (figs. 1 and 2) ranked high on the 

ARSG priority list for the largest trace-element loads in the 

upper Animas River watershed (Simon and others, 2001). 

It was suspected that water from Belcher Gulch (fig. 2) was 

infiltrating into the North Star Mine; however, the locaBy Winfield G. Wright and Bryan Moore
tions and amounts of infiltration were uncertain. In addition, 

scientific evidence was needed regarding the connection of 

Belcher Gulch to the North Star Mine before proceeding with 

an expensive infiltration-control remediation plan. 

The North Star Mine, which operated intermittently during 1882–1978, contains about 3 mi of underground tunnels. 

Historical records generally were not available, and the best 

information about the mine was obtained by oral communication with previous employees and mining engineers that 

worked in the mine. During the reconnaissance phase of this 

study, it was assumed that water discharging from the mine 

flowed freely through the mine. After the tracer-injection 

study had begun, oral communication with a previous mine 

employee revealed that a mine-drainage treatment system had 

been constructed inside the mine during the late 1970’s before 

the mine was sealed (the mine entrance was sealed by backfilling). This mine-drainage treatment system consists of an 

anoxic limestone drain, which contains several tons of limestone. In theory, the mine-drainage treatment system would 

improve acid mine drainage by increasing pH and causing dissolved metals to precipitate out of solution. Unfortunately, the 

system also could potentially remove constituents used during 

tracer-injection studies, thereby complicating interpretation of 

the tracer-injection results.

Description of Study Area

The upper Animas River watershed encompasses 146 mi2

of rugged mountainous terrain in the San Juan Mountains of 

southwestern Colorado. Altitudes range from 9,200 ft near the 

town of Silverton, Colo., to 13,800 ft at the summit of Niagara 

Peak (fig. 1). The upper Animas River watershed has three 

main branches upstream from Silverton—the Animas River, 

Cement Creek, and Mineral Creek. The upper Animas River is 

a southward-flowing tributary of the San Juan River, which is 

a major tributary of the Colorado River. The principal form of 

precipitation occurs as snow during November through May of 

each year, which can accumulate to 15 ft or more. Streamflow 

discharges can vary substantially, and about 80 percent of the 

annual runoff is derived from snowmelt, which occurs during 

May, June, and July of each year. For example, discharges in 

the Animas River downstream from Silverton can range from 

about 55 ft3/s during the low-flow period of late summer to 

3,000 ft3/s during snowmelt runoff of May-July.

The North Star Mine entrance is located along lower 

Mineral Creek downstream from the confluence of Belcher 

Gulch with Mineral Creek (fig. 2). The underground mine 

workings were known to penetrate beneath Belcher Gulch; 

however, there were several sources of water to the mine 

including a possible deep ground-water source that flows 

upward from a shaft in the mine, and a possible source of 

Figure 1. Location of the North Star Mine, Belcher Gulch, and other historical 

mines in the area, upper Animas River watershed, southwestern Colorado.

2 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

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water where the mine tunnels penetrate beneath the gulch 

(Steve Fearn, Fearn Engineering, Silverton, Colorado, oral 

commun., 2001). The principal source of water to the mine, 

however, is uncertain. It could be difficult to remediate the 

deep ground-water source, but it may be possible to remediate 

the source of water from the gulch. 

Other mines exist that may be physically connected to 

the North Star Mine through mine tunnels, or hydrologically 

connected through fractures that are common to the mineralized vein systems (Steve Fearn, Fearn Engineering, Silverton, 

Colorado, oral commun., 2001). The Sultan Mine (figs. 1 and 

2) is known to physically connect to the North Star Mine; 

however, the Sultan Mine is higher in the topography than the 

North Star Mine entrance, and it is uncertain whether there is 

a water connection. The Pittsburgh Mine (fig. 1) is known to 

trend in the direction of the North Star Mine because the same 

vein systems were being developed. The Pittsburgh Mine is 

lower in the topography than the North Star Mine entrance; 

Figure 2. Underground tunnels associated with the North Star, Sultan, and Gladstone mines, tracerinjection points, and sampling sites in the vicinity of Belcher Gulch.

Introduction 3

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hence, a water connection may be possible. The water must 

flow a long distance underground, however, for the connection 

to occur.

During snowmelt (high flow), discharge from Belcher 

Gulch can be high. The stream is known to flow to Mineral 

Creek during high flow; however, no discharge measurements 

have been made of Belcher Gulch during high flow. During 

low flow, water in Belcher Gulch disappears completely into 

the alluvium/colluvium as the stream flows down the mountain, and the stream does not flow to Mineral Creek. Springs 

are present in the alluvial fan at the bottom of Belcher Gulch, 

however, which may be the water that infiltrates into the 

alluvium. Alluvial fans typically occur at the bottom of alpine 

catchments, streamflow losses to alluvial fans are common, 

and springs typically occur at the downgradient (or downstream) end of the alluvial fans. 

Upstream from site E (fig. 2) is a waterfall (site D), and 

during September 2001, much more water was present in the 

stream above the waterfall than in the lower reaches. It was 

apparent from visual inspection that the stream was losing 

flow to the subsurface at many reaches along Belcher Gulch. 

It is unclear, however, whether the stream loses flow into the 

alluvium/colluvium of the alpine catchment, flowing down the 

canyon in the subsurface through the alluvium, or if the stream 

loses flow into underground mine structures. 

The mine-drainage treatment system in the North Star 

Mine was designed to remove trace elements; however, the 

system also could remove tracer-constituent concentrations 

introduced as part of this study. Several processes may be 

involved with mine-drainage treatment systems (Wildeman 

and Updegraff, 1997): (1) anaerobic biological processes, (2) 

sorption, (3) pH controls, (4) ion exchange, and (5) aerobic 

biological processes. Anaerobic biological processes can 

decrease trace-element concentrations through sulfate reduction, which precipitates sulfide minerals such as pyrite, and 

other trace elements can be coprecipitated with the pyrite. 

Reducing conditions are stimulated by the addition of organic 

matter to the mine-drainage treatment system. Trace-element 

concentrations can be decreased through sorption of trace elements to surfaces within the mine-drainage treatment system. 

Organic matter, rock substrate, and freshly precipitated iron 

oxyhydroxides can provide surfaces for sorption of trace 

elements. Trace-element concentrations can be decreased 

through pH controls, which is accomplished by the addition of 

limestone as the rock substrate in the mine-drainage treatment 

system. Limestone increases the pH, and trace elements such 

as aluminum, cadmium, copper, iron, and manganese are less 

soluble at higher pH values. Increasing the pH causes these 

trace elements to precipitate or sorb to the substrate in the 

mine-drainage treatment system. Trace-element concentrations can be decreased by ion exchange, where certain ions in 

the mine-drainage treatment system are exchanged for trace 

elements. After the mine drainage exits the anaerobic minedrainage treatment system, aerobic biological processes can 

decrease dissolved trace-element concentrations by precipitation, which includes iron and sulfur oxidation. In a literature 

search regarding mine-drainage treatment systems, no information was available on the removal rates of lithium, bromide, 

sodium, or chloride. From discussions with previous employees at the North Star Mine, it is believed that several tons of 

limestone was placed in the mine-drainage treatment system, 

and organic matter was not added to the system (Ernie Kuhn, 

Mayor, Town of Silverton, oral commun., 2001). 

Purpose and Scope

The purposes of this report are to determine (1) whether 

Belcher Gulch water is infiltrating into the backside of the 

North Star Mine, (2) where along Belcher Gulch the water 

is infiltrating, (3) possible hydraulic connections between 

Belcher Gulch to other historical mines in the area, and (4) 

ground-water residence times and characteristics of tracer 

recovery curves from the injection point to the North Star adit. 

If it is demonstrated that Belcher Gulch water infiltrates into 

the backside of the North Star Mine, possible remediation 

steps might include routing the stream around the mine workings, construction of a grout curtain to prevent infiltration, or 

lining the channel.

Tracer-injection techniques were used to determine 

whether the principal source of water to the North Star Mine 

was caused by infiltration of surface water from Belcher 

Gulch into the mine. The tracer-injection studies were 

designed to determine where along Belcher Gulch the stream 

infiltrates into the mine. The study also was to determine 

whether water from Belcher Gulch flows to other mines in the 

area. If it is demonstrated that Belcher Gulch water infiltrates 

into the North Star, remediation measures may be undertaken 

to decrease the discharge of water from the mine, thereby 

reducing trace-element loads. 

Reconnaissance for the tracer-injection studies was done 

during August to September 2001, and baseline samples were 

collected during September 10 and 11, 2001. The tracerinjection studies were done during September 15 through 

October 11, 2001. Water samples were collected for tracerrelated constituents from September 15 through 

November 1, 2001. This work was done by the U.S. 

Geological Survey in cooperation with the Animas River 

Stakeholders Group (ARSG) and San Juan County, Colo. 

Previous Studies

Water-Quality Sampling

As part of the USGS Abandoned Mine Lands Initiative (AMLI), water-quality samples were collected from the 

North Star Mine on a monthly or seasonal basis for 1 year 

during 1997–98 (Mast and others, 2000). Water draining from 

the North Star Mine has a relatively high pH that fluctuates 

4 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado
between 6.18 and 7.33 (fig. 3); however, historical observations indicated that the water has been very acidic (Ransome, 

1901). The mine-drainage treatment system, even though it 

was constructed during the late 1970’s, continues to raise the 

pH of the mine drainage. Dissolved-zinc concentrations in 

water from the mine, even in the presence of the treatment 

system, are high (fig. 3), and concentrations of other elements 

such as iron also are high (Mast and others, 2000). During 

1997–98, baseline dissolved-sodium concentrations at the 

North Star Mine ranged from 4.08 to 6.37 mg/L (Mast and 

others, 2000); analyses were not done for dissolved bromide, 

lithium, or chloride. Discharge from the North Star Mine 

ranged from about 0.4 to 1.2 ft3/s (fig. 3). It is difficult to 

determine the timing of the peak discharge at the North Star 

Mine because of the intermittent measurements; however, data 

from other historical mine sites monitored in the watershed 

indicate a 1- or 2-month delay between the snowmelt runoff 

in streams and increasing discharges from mines (Wright 

and others, 1998; Mast and others, 2000). This delay may 

be caused by recharge of the ground-water system by snowmelt and slow movement of ground water to the mines that 

were monitored. Some of the mines monitored did not show 

any discharge fluctuations, indicating that some mines may 

intersect fractures from deep ground-water systems that are 

isolated from the seasonal fluctuations.

Surface Geophysics

A surface geophysical survey was done in Belcher Gulch 

for the Bureau of Land Management (BLM) as part of the 

AMLI, and the work was published by Ackman and others 

(1998). Electromagnetic conductivity (EM) and Very Low 

Frequency (VLF) surveys were done in the reach of Belcher 

Gulch where voids from the underground mine workings 

might be present. The surface geophysical traverse of this 

reach is shown in figure 4. Results of the EM survey indicated 

that there are three anomalies in the subsurface: (1) from 290 

to 320 m, (2) from 420 to 450 m, and (3) from 470 to 

500 m. The latter two anomalies probably resulted from metallic objects buried in the alluvium. Results of the VLF survey 

indicated that there are two anomalies: (1) from 50 to 100 m, 

and (2) from 250 to 380 m. The traverse segment from 50 to 

Nov-98

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DISSOLVED ZINC, 

IN MICROGRAMS PER LITER

pH

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Nov-97 Jan-98 Mar-98 Apr-98 June-98 Aug-98 Sept-98

pH, IN STANDARD UNITS

Nov-98

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400

600

800

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1,200

1,400

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ANIMAS RIVER DISCHARGE,

IN CUBIC FEET PER SECOND 

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0.4

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Nov-97 Jan-98 Mar-98 Apr-98 June-98 Aug-98 Sept-98

NORTH STAR DISCHARGE,

IN CUBIC FEET PER SECOND 

North Star Mine discharge

Streamflow discharge,

 Animas River below

 Silverton

Figure 3. Discharge, pH values, and dissolved-zinc concentrations in water 

from the North Star Mine, December 1997 through October 1998.

Introduction 5
100 m indicated the presence of a highly conductive geologic 

feature such as a vein of sulfide minerals or fractures filled 

with conductive liquid such as acid mine drainage (Ackman 

and others, 1998, p. 10). The cross section of the VLF data 

indicated a fracture zone dipping toward the southwest. The 

anomaly from 250 to 380 m was broad and indicative of fractures filled with freshwater. This anomaly probably extends to 

depths of at least 60 m and was observed near the subsurface 

location of the North Star vein (fig. 2). Anomalies were considered to represent open underground voids.

Methods of Study

To evaluate whether surface water in Belcher Gulch 

might be infiltrating into the North Star Mine, a salt- and dyetracing approach was used. In order to pinpoint the location 

where the stream infiltrates into the mine, tracer-injection tests 

were done from four sites in Belcher Gulch: (1) the southern branch of Belcher Gulch immediately upstream from the 

confluence with the northern branch and upgradient from the 

underground mine workings (fig. 2, site E); (2) between the 

locations where major vein structures were mapped in the 

underground mine workings (fig. 2, site G); (3) downstream 

from most of the underground tunnels and mine workings 

(fig. 2, site H); and (4) at a high-altitude location on the southFigure 4. Aerial photograph showing surface geophysical traverse done in 

Belcher Gulch by Ackman and others (1998). 

6 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

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ern branch of Belcher Gulch (fig. 2, site B). Different tracer 

solutions were used for the different injection sites described 

above: (1) lithium bromide (LiBr at site E); (2) optical 

brightener dye (Tinopal CBS-X at site G); (3) sodium chloride (NaCl at site H); and (4) sodium chloride (NaCl at site 

B). Laboratory analytical methods, calibration of analytical 

instruments, calculation of concentration errors, and qualityassurance data are presented in the Appendix at the end of this 

report. 

Tracer-Injection Methods

Continuous-Injection Tests 

The first tracer-injection test used saturated lithium bromide (LiBr) as the tracer solution, and dissolved lithium and 

bromide were the target tracer constituents. A bromide ionselective electrode was placed in the North Star Mine drainage 

to detect any breakthrough of the tracer solution. On 

September 14 to 15, pumps, batteries, solar battery charger, 

portable water tank, and LiBr powder were carried up Belcher 

Gulch. The LiBr injection site E was located on a 25-degree 

slope in the southern branch (fig. 5, site E). About 60 gal 

of stream water was placed in the portable tank and mixed 

with 53.5 lb of LiBr for an injectate concentration of 11,190 

mg/L as Li. Pumping of the LiBr tracer solution began on 

September 15, 2001, at 1:25 p.m. and continued for 24 hours 

at a pumping rate of 67.5 + 1.3 mL/min. Injection rates and 

battery voltages were monitored overnight. Concentration of 

lithium in the stream downstream from the confluence (fig. 2, 

site F) was 315 μg/L. Pumping ceased on September 16 at 2:

20 p.m. Dissolved-lithium and dissolved-bromide concentrations were analyzed in water samples collected from the North 

Star mine for this injection test.

The second tracer-injection test used optical brightener 

dye (Tinopal CBS-X) as the tracer solution, and the fluorescent dye was the target tracer constituent. On September 16, 

the equipment was transferred to site G (fig. 5), and 70 gal 

of stream water was placed in the portable water tank and 

mixed with 14.3 lb of dye for an injectate concentration of 

25,000 mg/L. A metal pipe, or well point, was driven about 

3 ft into the alluvium to facilitate the injection of the dye into 

the subsurface (fig. 5). Pumping of the dye tracer solution into 

the metal pipe began on September 17, 2001, at 3:20 p.m. and 

continued for about 24 hours at a pumping rate of 

50 + 1.5 mL/min. Injection rates and battery voltages were 

monitored overnight. Concentration of dye in the stream 

300 ft downstream from the injection point was 38.5 mg/L, 

or a relative fluorescence of 200 units. Water samples collected from the North Star Mine entrance during dye injection 

were qualitatively examined for the presence of dye by using 

a battery-operated ultraviolet (UV) light. Pumping ceased on 

September 18 at 3:15 p.m.

The third tracer-injection test used saturated sodium 

chloride (NaCl) as the tracer solution, and dissolved sodium 

and chloride were the target tracer constituents. On September 

18, the equipment was transferred to site H (fig. 5), and 80 gal 

of stream water was placed in the portable water tank and 

mixed with 135.5 lb of NaCl for an injectate concentration of 

98,349 mg/L as Na. Pumping of the NaCl tracer solution into 

the stream began on September 19, 2001, at 12:00 p.m. and 

continued at a pumping rate of 200 + 1.6 mL/min for about 

12 hours when the injection pump failed. The dissolvedsodium concentration was 171 mg/L downstream from the 

injection site. Dissolved sodium and dissolved chloride were 

analyzed in water samples collected from the North Star Mine 

for this injection test.

Slug-Injection Test

The initial design of the fourth tracer-injection test was to 

carry the equipment up the Belcher Gulch canyon to site B and 

inject saturated NaCl into the stream over a 24-hour period. 

On October 11, 2001, NaCl was carried up the mountain; 

however, unexpected winter conditions prevented a standard 

tracer-injection test from being done. Instead of injecting the 

NaCl solution over a 24-hour period, 50 lb of NaCl was slowly 

poured into the stream over a period of 1 hour at site B. A true 

slug-injection might be defined as the instantaneous dumping 

of a tracer solution into the stream (Mull and others, 1988; 

Gospodaric and Habic, 1976); however, pouring of the NaCl 

into the stream during a 1-hour period is more similar to a 

slug-injection test than it is to a continuous-injection test. The 

dissolved-sodium concentration was 524 mg/L at site B downstream from the slug-injection location. Dissolved-sodium 

concentrations were analyzed in water samples collected from 

the North Star Mine for this injection test; dissolved-chloride 

concentrations were not analyzed.

Sample Collection

An automatic sampler was placed at the North Star Mine 

entrance (fig. 2, site K) to sample intermittently during and 

after injection of the tracer solutions. During September 15 

through 20, the automatic sampler was set to collect 1 L of 

water from the mine entrance at 2-hour intervals. During 

September 20 through November 1, the sampler was set 

to collect samples at 7-hour intervals. Water samples were 

collected from the high-altitude northern branch (site A), 

the high-altitude southern branch (site B), Belcher Gulch 

downstream from the confluence of the northern and southern 

branches (site F), Belcher Gulch downstream from the Level 4 

tunnel (site I), the spring in the Belcher Gulch alluvial fan 

(site J), Sultan Mine drainage at the North Star road (site 

L), Sultan Mine (site M), and the Pittsburgh Mine (fig. 1). 

Additional samples were collected from the North Star Mine 

entrance during the injection tests for real-time monitoring of 

Methods of Study 7
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Southern Branch

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Figure 5. Tracer-injection test locations in Belcher Gulch.

8 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado
bromide and chloride concentrations and qualitative dye detection. In all, more than 200 water samples were collected as 

part of this study, and more than 340 laboratory analyses were 

done on these samples.

Most of the samples were filtered through 0.45-μm 

capsule filters into 250-mL plastic bottles; some samples were 

decanted from the 1-L automatic sampler bottle into 250-mL 

plastic bottles without filtration. Samples for lithium and 

sodium analyses were acidified using nitric acid. For the dye 

analyses, the samples were filtered through 0.45-μm syringe 

filters and were not acidified. Samples for dye analyses are 

frequently analyzed unfiltered; however, the iron oxyhydroxide precipitates in water from the North Star Mine interfered 

with the fluorometric analyses; hence, the samples were 

filtered.

Discharge Determinations

Quantification of the discharges in streams in the study 

area was done to describe the flow losses in Belcher Gulch, 

and whether the flows were lost to the alluvial fan or the 

ground-water system, which may then flow to the North Star 

Mine. Because of the variable nature of the high-altitude 

stream, several types of discharge-measurement techniques 

were used. A pygmy meter was used when an open channel 

was present, and there was adequate water for measurement 

(for example, sites G, H, and K, fig. 2). For small volumes of 

water in an open channel and discharge from springs, volumetric measurements were made (for example, sites I and J). 

At site A, the channel was filled with rocks (fig. 6); at site B, 

ground water was emanating over a 100-ft-wide area 

(fig. 6). Therefore, discharge was determined at these sites 

by using spot-injection tests. A staff gage was installed at the 

North Star Mine entrance (site K) so frequent stage readings 

could be taken, and the stage readings were referenced to 

discharge measurements. 

Errors for pygmy meter measurements can be on the 

order of +10 percent and can be greater in mountain streams 

with turbulent flows and irregular cross sections (Rantz, 

1982). The volumetric measurements were done using a 2-gal 

plastic bag that was calibrated and graduated to indicate the 

fill volumes; the time taken to fill the bag was measured using 

a stopwatch, and discharge was determined by the volume 

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Figure 6. The high-altitude northern branch (site A) and southern branch (site B) of Belcher Gulch.

Methods of Study 9
filled per unit of time. Errors on volumetric flow measurements are very small, and this method provides the most 

accurate estimate for discharge of flows from small mountain 

streams and small mine discharges (Rantz, 1982). 

During the spot-injection tests, the northern branch 

(site A) was flowing underneath rocks and boulders that filled 

the channel (fig. 6). The stream could not be accessed except 

by removing rocks, and only part of the stream could then be 

accessed after removing rocks. In the southern branch (site B), 

ground water was discharging from bedrock, boulders, mossy 

areas, and alpine grass clumps amongst dead trees placed 

by avalanches (fig. 6). Slopes were greater than 30 degrees 

at site B. Streamflow measurement of these high-altitude 

streams would be impossible using conventional methods. 

In order to quantify the amount of water in the high-altitude 

streams for comparison to the lower reaches, a small pump, 

battery, solar panel, and 1,000 g of tracer salt were used to 

make spot-injection tests to determine streamflow discharge. 

Saturated potassium chloride (KCl) was used as the spot-injection solution, dissolved potassium was the target constituent, 

and discharge was determined through dilution of the potassium by the streamwater. A chloride probe was placed in the 

streams downstream from the injection sites to determine 

when the tracer reaches had become fully mixed. After analyzing dissolved-potassium concentrations in the laboratory, the 

equation for the conservation of mass was used to make the 

discharge determination: 

 Qs=QpCp/(Cs–Cb)

where: 

Qs is unknown streamflow discharge,

Qp is injection-pump discharge,

Cp is spot-injection solution concentration,

Cs is dissolved-potassium concentration in the stream 

downstream from the injection point, and

Cb is baseline dissolved-potassium concentration in the 

stream prior to the injection test.

At the northern branch site A, the injection solution was 

pumped directly into the stream through a cleared space in the 

rocks (fig. 6). The sample was collected for the tracer solution through another cleared space in the rocks about 300 ft 

downstream from the injection site. Water in the southern 

branch discharged over a 100-ft reach (fig. 6), and the tracer 

solution was injected into one of these water sources. About 

300 ft downstream from the injection site, the stream narrows 

down to a 10-ft-wide channel where an equal-width-integrated 

sample was collected for determination of the tracer-constituent concentration. In general, errors on spot-injection discharge measurements are relatively small compared to pygmy 

meter measurements (Rantz, 1982), and the errors are limited 

to analytical determinations of the tracer constituent in the 

laboratory.

Interpretation of Tracer-Injection Data

Performing a tracer-injection test in underground mines 

is similar to tracer-injection tests in naturally occurring 

underground caves. There may be combinations of free-flowing streams, calm pools, waterfalls, slow movement through 

water-filled fractures, and mixing with other water sources. 

There also may be sediments or gravels that can retain tracer 

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Figure 7. Hypothetical example of tracer recovery curve showing breakthrough, 

peak concentration, and receding concentrations of tracer constituent.

10 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado
constituents, slowing the recovery of the tracer, resulting in 

attenuation of the tracer. Attenuation of the tracer also can be 

caused by chemical reaction of the tracer with other constituents in the water, and by reaction with the mine-drainage 

treatment system. A hypothetical example of a tracer recovery 

curve is shown in figure 7. Tracer constituents in ground-water 

systems typically show an initial “breakthrough,” which is the 

indication of the arrival of the tracer constituent (similar to the 

rising limb of a streamflow hydrograph, fig. 7). The “residence 

time,” or traveltime of the bulk of the tracer-constituent mass, 

is typically indicated by the time from the beginning of injection to the peak concentration of the tracer constituent (fig. 7) 

(Mull and others, 1988; Gospardic and Habic, 1976). 

For this study, the positive indication of tracer recovery is 

indicated by the tracer breakthrough. The receding concentrations of the tracer-recovery curve (fig. 7) might show a gradual 

decrease of tracer concentrations, which is caused by tracer 

retention in sediments, the tracer residing in pools or eddies, or 

ground-water velocities limited by low-permeability fractures. 

Much information can be derived from the characteristics of 

the tracer-recovery curve. For example, a sharp peak and rapidly receding concentrations can indicate little or no storage in 

the ground-water system; the tracer moves through the system 

virtually uninhibited. A broad peak and gradual decline of the 

receding concentrations can indicate slow ground-water velocities or ample storage capacity in the aquifer. Multiple peaks 

of the tracer-recovery curve can indicate multiple flow paths 

for tracer movement through the ground-water system, where 

the different flow paths have different residence times. In this 

study, the mine-drainage treatment system might attenuate 

different tracer constituents at different rates, such that a more 

soluble constituent (or a constituent less subject to removal by 

the treatment system) might exhibit a more rapid breakthrough 

than a more reactive tracer constituent. As a result of these 

characteristics, the tracer-recovery curves are complex and are 

difficult to interpret.

Baseline concentrations of tracer constituents should have 

been analyzed for a lengthy period prior to the injection tests. 

However, during summer of 2001, the study area had above 

average rainfall, and the hydrologic conditions were variable; 

hence, baseline samples would not have been representative of 

the tracer period. For this study, samples were collected during 

the period of the tracer-injection study, were analyzed in the 

laboratory, and the range of analytical uncertainty (or analytical error) determined for each data point (see “Laboratory 

Analytical Methods” section in the Appendix). The data were 

plotted on time-series graphs, examined for baseline-like values, and the averages and standard deviations of baseline-like 

values were determined. Some of the data exhibited downward 

trends on time-series graphs during the tracer period; therefore, the baseline-like values were represented by sloped lines. 

The standard deviations were multiplied by 2 to graphically 

depict envelopes of the plus-or-minus 2-times the standard 

deviation (or +2-sigma) of the baseline-like values. The criteria for determination of tracer breakthrough consisted of tracer 

concentrations where the range of uncertainty of individual 

sample concentrations exceeded the +2-sigma envelope. 

Results of Tracer Recovery and 

Discharge Measurements

Six tracer-injection tests were done as part of this study. 

Four of the tracer-injection tests—three continuous-injection 

and one slug-injection test—were done to identify possible 

hydrologic connections between Belcher Gulch and mines 

in the area. Two of the tracer-injection tests were done as 

spot-injection tests to determine streamflow discharge in 

high-altitude alpine streams. For the connections between 

Belcher Gulch and the mines, samples were collected from 

water flowing from mine entrances located thousands of feet 

or miles (in the case of the Pittsburgh Mine) downgradient 

from the injection sites. For spot-injections tests, samples were 

collected from the streams just a few feet downstream from 

the injection sites.

Tracer Recovery at the North Star Mine

Continuous-Injection Tests

Injection of lithium bromide began at site E on 

September 15, 2001, at 1:25 p.m. Dissolved-lithium concentrations in water from the North Star Mine fluctuated during 

the sampling period, possibly because of low concentrations 

and analytical uncertainty at low concentrations, and possibly 

because lithium was being attenuated by the mine-drainage 

treatment system. Dissolved-lithium concentrations exceeded 

the +2-sigma envelope during several periods after injection 

began—at 12.5, 50.5, 64.5, and 86.5 hours (fig. 8); however, 

the range of uncertainty at 64.5 hours did not exceed the envelope. The causes of the different breakthroughs are unknown 

but may have been caused by multiple ground-water flow 

paths resulting in different lithium breakthroughs. The early 

breakthroughs of elevated lithium could indicate slight inflows 

at certain locations, and the larger sustained breakthrough of 

elevated lithium (86.5 hours) could indicate a larger amount of 

infiltration at a different location. The breakthrough at 

86.5 hours was sustained for about 2 to 3 days, indicating 

that there is ample amount of water storage in the mine or the 

tracer was retained in sediments and pools.

Similar to the lithium-recovery curve, dissolved-bromide 

concentrations exceeded the +2-sigma envelope during several 

periods after injection began—at 12.5, 50.5, 64.5, and 

86.5 hours (fig. 8); however, the range of uncertainty at 

50.5 hours did not exceed the envelope. In general, the dissolved-lithium and dissolved-bromide recovery curves have 

similar characteristics except that the dissolved-bromide 

Methods of Study 11
curve has a downward slope and the dissolved-lithium curve 

does not (fig. 8). It is uncertain why the dissolved-bromide 

recovery curve shows a downward slope and the dissolvedlithium curve does not. Tracer breakthroughs of both lithium 

and bromide tracer constituents substantiate a surface-water 

and ground-water connection between Belcher Gulch and the 

North Star Mine. The numerous breakthroughs indicate multiple ground-water flow paths; however, there are differences 

in the magnitude of the concentration increases, which may 

have been caused by the mine-drainage treatment system or 

reactions of the tracer constituents with acid mine drainage.

Injection of the optical brightener dye began at site G on 

September 17, 2001, at 3:20 p.m. Because there are no baseline dye concentrations, the 2-sigma approach was not applied 

Figure 8. Dissolved-lithium and dissolved-bromide concentrations in water from the North Star 

Mine after injection began at site E.

12 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

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to the dye-recovery data. About 24 hours after injection began, 

a slight fluorescence was observed using a hand-held UV light 

in water samples collected from the North Star Mine entrance. 

From laboratory analyses, an increase of dye concentration 

was measured at about 23 hours after injection began (fig. 9). 

The dye recovery curve lasted about 2 to 3 days, which was 

similar to the broad lithium concentration peak after 

86.5 hours (fig. 8). Because there were no early dye breakthroughs (fig. 9), it is possible that the larger quantity of water 

from Belcher Gulch flows into the mine downstream from site 

G, and the location of the smaller inflows were upstream from 

site G. Optical brightener dye is not as easily degraded by acid 

conditions as are the other types of dye; however, acid mine 

drainage and mine-drainage treatment systems provide conditions not typically experienced in nature. Therefore, the dye 

concentrations and recovery times are not as reliable as the 

lithium and bromide tracer-recovery data. 

Injection of sodium chloride began at site H on 

September 19, 2001, at 12:00 p.m. After about 12 hours, the 

injection pump failed, but a sufficient amount of tracer solution was injected into the stream to accomplish a tracer study. 

Dissolved-sodium concentrations at the North Star Mine 

showed a slight increase about 18 hours after injection began 

(fig. 10); however, the concentration increase was small and 

the range of uncertainty was not greater than the +2-sigma 

envelope (fig. 10). Dissolved-chloride concentrations showed 

a slight increase about 14 hours after injection began; however, 

the increase was small and the range of uncertainty was not 

greater than the +2-sigma envelope. Hence, there are no conclusive results indicating that tracer constituents flowed into 

the mine from injection at site H. Therefore, with the positive 

tracer recoveries of lithium and bromide from site E, and positive recovery of optical brightener from site H, it is believed 

that little, if any, water flows into the mine downstream from 

site G.

Slug-Injection Test 

The fourth tracer-injection test was performed from 

the high-altitude stream (site B), on the southern branch of 

Belcher Gulch at about 11,000 ft above sea level (fig. 2, 

fig. 6). A 50-lb bag of NaCl was poured into the stream at 

a constant rate during a 1-hour period on October 11, 2001, 

beginning at 1:00 p.m. A slight increase of dissolved-sodium 

concentration was detected in water from the North Star Mine 

about 35 hours after injection began (fig. 11); however, the 

increase was not greater than the +2-sigma envelope. Several other increases occurred at about 10, 11, 15, and 16 days 

after injection began (fig. 11), and some of the increases were 

greater than the +2-sigma envelope. Tracer breakthrough of 

dissolved sodium further substantiates a surface-water and 

ground-water connection between Belcher Gulch and the 

North Star Mine, and numerous tracer breakthroughs support 

the hypothesis of multiple infiltration locations.

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FIgure 9. Optical brightener dye concentrations in water from the North Star Mine after 

injection began at site G.

Results of Tracer Recovery and Discharge Measurements 13
Tracer Recovery at Other Sites

Water samples were collected intermittently from the 

Pittsburgh Mine (fig. 1), the Sultan Mine (figs. 1 and 2), and 

from springs in the alluvial fan at the bottom of Belcher Gulch 

(fig. 2, site J). In retrospect, interpretation of tracer concentrations from intermittent samples was inconclusive. Dissolvedlithium concentrations in water from the Pittsburgh Mine 

increased slightly after the LiBr injection began at site E 

(fig. 12); however, the increase was only about 2 μg/L and 

within the range of natural variability. Dissolved-sodium 

concentrations in water from the Pittsburgh Mine increased 

slightly after the NaCl injection began at site H and after NaCl 

injection began at site B (fig. 12); however, the increases were 

small and within the range of natural variability. These results 

show no conclusive evidence of a surface-water and groundwater connection between Belcher Gulch and the Pittsburgh 

Mine. 

Dissolved-lithium concentrations in water from the 

Sultan Mine increased slightly after the LiBr injection began 

at site E (fig. 13); however, the increase was only about 3 μg/L 

Figure 10. Dissolved-sodium and dissolved-chloride concentrations in water from the North Star 

Mine after injection began at site H.

14 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

SODIUM AFTER INJECTION BEGAN AT SITE H

CHLORIDE AFTER INJECTION BEGAN AT SITE H

EXPLANATION

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Results of Tracer Recovery and Discharge Measurements 15

Figure 11. Dissolved-sodium concentrations in water from the North Star Mine after injection began 

at site B.

SODIUM AFTER INJECTION BEGAN AT SITE B

EXPLANATION

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and within the range of natural variability. Dissolved-sodium 

concentrations in water from the Sultan Mine increased 

slightly after the NaCl injection began at site H; however, the 

increase was small and within the range of natural variability. 

Dissolved-sodium concentrations did not increase in water 

from the Sultan Mine after NaCl injection began at site B. 

These results show no conclusive evidence of a surface-water 

and ground-water connection between Belcher Gulch and the 

Sultan Mine. 

During low flow, water in Belcher Gulch disappears 

completely into the alluvium/colluvium as the stream flows 

down the mountain, and the flow quantities become less as the 

stream flows down valley (see “Discharge of Streams, Springs, 

and Mine Outflows” section). At the bottom of Belcher Gulch, 

at Mineral Creek, a spring discharges from the alluvial fan 

(fig. 2, site J). Dissolved-sodium concentrations in water from 

the spring increased from 1.7 to 2.0 mg/L after the NaCl injection began at site H (fig. 14), and dissolved-sodium concentrations increased from 2.7 to 3.2 mg/L after NaCl injection 

began at site B (fig. 14). These results indicate a surface-water 

and ground-water connection between Belcher Gulch and the 

spring in the Belcher Gulch alluvial fan.

Discharge of Springs, Streams, and Mine 

Outflows

 During the reconnaissance phase of this study (late 

August through early September 2001), discharge measurements were made at the North Star Mine and other mines 

in the area, in Belcher Gulch, and at springs near Mineral 

Creek (table 1). After the first three tracer-injection tests were 

completed, discharge synoptic measurements were done on 

September 27 to 28 where discharges were measured at all 

the sites in Belcher Gulch for quantification of streamflows 

(table 1, under the heading “Discharge Synoptic Measurements”). The spot-injection test method was used to measure 

discharges in the high-altitude streams (sites A and B), and 

pygmy meter and volumetric measurements were made at 

the other sites. At the high-altitude sites, the discharges of 

the southern and northern branches were 0.32 and 0.23 ft3/s, 

respectively, for a total of 0.55 ft3/s at the headwaters of 

Belcher Gulch (table 1). Discharge of the northern branch 

upstream from the confluence (site C) was 0.14 ft3/s. Below 

the waterfall (site D), the discharge of the southern branch was 

0.24 ft3/s, for a total of 0.38 ft3/s in both branches, indicating 

that 0.17 ft3/s was probably percolating downvalley as under-
16 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorado

Figure 12. Dissolved-lithium and dissolved-sodium concentrations in water from the Pittsburgh 

Mine.

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Surface-Water and Ground-Water Interactions at the North Star Mine 17

Figure 13. Dissolved-lithium and dissolved-sodium concentrations in water from the Sultan Mine.

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18 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorad

Figure 14. Dissolved-sodium concentrations in water from the spring in the Belcher Gulch alluvial fan.

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flow through the alluvium/colluvium. Downstream from the 

confluence (site F), the discharge was 0.18 ft3/s. Below the 

Level 4 tunnel (site I), discharge was 0.14 ft3/s, indicating an 

additional loss of streamflow. The stream completely disappeared just downstream from site I. In the springs at Mineral 

Creek (site J), the discharge was 0.05 ft3/s. Some of the water 

between the Level 4 tunnel and the springs might have been 

lost to evapotranspiration through willows and shrubs in the 

alluvial fan. 

In most hydrologic systems, and particularly in alpine 

catchments, discharge typically increases in a downgradient direction because the water table comes closer to land 

surface, and the drainage area of the catchment increases in a 

downstream direction. Accordingly, the 0.55-ft3/s discharge 

measured at the headwaters of Belcher Gulch should have 

increased substantially toward the downstream end of the 

catchment. However, there was a discharge loss of about 

91 percent of the streamflow (0.50 ft3/s). Discharge from the 

North Star Mine was relatively steady at 0.82 ft3/s, as it had 

been for the duration of the tracer-injection study. The discharge synoptic illustrated that a substantial amount of water 

was lost to the ground-water system at several locations along 

Belcher Gulch. The surface geophysical study done by Ackman and others (1998) indicated the presence of underground 

voids in several locations, which also supports the hypothesis 

that water in Belcher Gulch could be flowing into the mine at 

several locations. 

Surface-Water and Ground-Water 

Interactions at the North Star Mine

From the tracer-injection tests and the discharge synoptic, 

a conceptual model of surface-water and ground-water interactions between Belcher Gulch and the North Star Mine was 

developed (fig. 15). Water flows from the high-altitude site, 

southern branch (site B), and down the waterfall. Just below 

the waterfall (site D), part of the water infiltrates into the 

alluvium and part of the water remains on the surface in the 

channel. The water in the alluvium flows at a relatively slower 

rate compared to the surface water. Water in the alluvium 

flows into fractures that may be connected to the underground 

mine workings near the Crown Point vein (figs. 2 and 15). 

Farther down the valley, water in the alluvium flows into larger 

fractures that are connected to the mine. Most of the water 

probably flows into the mine between sites G and H, which 

are directly over the vertical shaft (raise) between the Level 7 

and the Level 4 tunnels (Steve Fearn, Fearn Engineering, oral 

commun., 2001).

When a tracer is injected into the stream where the 

alluvium is present, such as during the LiBr injection (fig. 15), 

the tracer does not infiltrate immediately to the bottom of the 

alluvium. Instead, the tracer may migrate from the stream into 

the alluvium, where it becomes dispersed along this flow path, 

and some of the tracer may eventually flow into the mine. On 

the other hand, the NaCl tracer solution injected at the top of 
Surface-Water and Ground-Water Interactions at the North Star Mine 19

Table 1. Discharge measurements of water from springs, streams, and mine outflows.

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Site letter

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Stage

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Discharge 

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North Star Mine

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Belcher Gulch

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Pittsburgh Mine (?)

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Figure 15. Schematic cross section of surface-water and ground-water interactions between Belcher Gulch and the 

North Star Mine.

the waterfall, such as during the fourth tracer test, may flow 

into the alluvium just below the waterfall and percolate down 

the valley through the alluvium. Flow rates are slower along 

this pathway, and infiltration of this tracer into the mine may 

be substantially delayed. This tracer possibly infiltrated into 

the North Star Mine at several locations along Belcher Gulch, 

as indicated by the multiple tracer peaks observed on the tracer 

recovery curve (for example, fig. 11). 

Summary

Tracer-injection studies were done to determine whether 

water flows from Belcher Gulch into the North Star Mine and 

other mines in the upper Animas River watershed, southwestern Colorado. The tracer-injection studies also were designed 

to determine where along Belcher Gulch the water flows into 

the mine. Four separate tracer-injection tests were done using 

lithium bromide (LiBr), optical brightener dye, and sodium 

chloride (NaCl) as tracer solutions. Two of the tracers (LiBr 

and dye) were injected continuously for 24 hours, one of the 

NaCl tracers was injected continuously for 12 hours, and one 

of the NaCl tracers was injected over a period of 1 hour. More 

than 200 water samples were collected from the North Star 

Mine by an automatic sampler. Samples were collected from 

the Pittsburgh Mine, the Sultan Mine, Belcher Gulch, and 

springs in the Belcher Gulch alluvial fan near Mineral Creek. 

Laboratory analyses were done for target tracer constituents 

of dissolved lithium, optical brightener dye, dissolved sodium, 

dissolved bromide, and dissolved chloride. 

Concentration increases of tracer constituents were 

detected in water discharging from the North Star Mine, 

substantiating a surface-water and ground-water connection 

between Belcher Gulch and the North Star Mine. Different 

timing and magnitude of tracer breakthroughs indicated multiple flow paths with different residence times from the stream 

to the mine. Small quantities of water may flow into the mine 

through small fractures, and larger quantities of water may 

20 Application of Tracer-Injection Techniques to Demonstrate Surface-Water and Ground-Water Interactions Between an 

 Alpine Stream and the North Star Mine, Upper Animas River Watershed, Southwestern Colorad
References Cited 21

flow into the mine through large fractures, as indicated by different sharp and broad tracer-recovery peaks. Smaller quantities of water may be flowing into the mine through the Crown 

Point vein (between sites E and G), and the larger quantities 

of water may be flowing into the mine near the raise from the 

Level 7 to the Level 4 tunnels (between sites G and H). Tracer 

breakthroughs were inconclusive in water from the Pittsburgh 

and Sultan Mines. 

Discharge synoptic measurements indicated that nearly 

all of the water in Belcher Gulch is lost to the ground-water 

system before reaching Mineral Creek, and this quantity of 

water loss (about 0.50 ft3/s) may be flowing into the North Star 

Mine. From the tracer tests and discharge synoptic, a conceptual model was developed for surface-water and ground-water 

interactions between Belcher Gulch and the North Star Mine. 

This information, combined with previous surface geophysical 

surveys indicating the presence of subsurface anomalies, may 

assist with decision-making processes for the prevention of 

infiltration into the mine and remediation of mine drainage.

References Cited

Ackman, T.E., Hammack, R.W., and Veloski, G.A., 1998, 

Geophysical investigation of selected stream segments in 

the upper Animas River watershed, San Juan County, Colorado, to identify potential water-loss zones: U.S. Department of Energy, Federal Technology Center, Pittsburgh, Pa., 

15 p.

Gospodaric, Rado, and Habic, Peter, eds., 1976, Underground 

water tracing—Investigations in Slovenia: Institute for Karst 

Research, Postojna, Yugoslavia, 305 p.

Long, H.K., Daddow, R.L., and Farrar, J.W., 1998, U.S. 

Geological Survey Standard Reference Sample 

Project—Performance evaluation of analytical laboratories: U.S. Geological Survey Fact Sheet FS–031–98 April 

1998, http://btdqs.usgs.gov/srs/FS_031_98.html, accessed 

December 12, 2001.

Mast, M.A., Evans, J.B., Leib, K.J., and Wright, W.G., 2000, 

Hydrologic and water-quality data at selected sites in the 

upper Animas River watershed, southwestern Colorado, 

1997–99: U.S. Geological Survey Open–File Report 00–53, 

20 p., 1 plate, CD-ROM.

Mull, D.S., Smoot, J.L., and Liebermann, T.D., 1988, Dye 

tracing techniques used to determine ground-water flow in 

a carbonate aquifer system near Elizabethtown, Kentucky: 

U.S. Geological Survey Water-Resources Investigations 

Report 87–4174, 95 p., 1 plate.

Ransome, F.L., 1901, Economic geology of the Silverton 

quadrangle, Colorado: U.S. Geological Survey Bulletin 

182, 265 p.

Rantz, S.E., 1982, Measurement and computation of streamflow: v 1. Measurement of stage and discharge: U.S. 

Geological Survey Water–Supply Paper 2175, 284 p.

Simon, William, Butler, Peter, and Owen, J.R., 2001, Use 

attainability analysis for the Animas River watershed: 

Animas River Stakeholders Group, 240 p., appendixes, CDROM, http://www.waterinfo.org/arsg/main.html. 

Taylor, J.K., 1987, Quality assurance of chemical measurements: Chelsea, Mich., Lewis Publishers, Inc., 328 p.

Wildeman, T.R., and Updegraff, David, 1997, Passive bioremediation of metals and inorganic contaminants in

Macalady, D.L., ed., Perspectives in environmental 

chemistry: United Kingdom, Oxford University Press, 

p. 473–495.

Wright, W.G., Leib, K.J., and Mast, M.A., 1998, Seasonal 

fluctuations of discharge and dissolved constituents from 

selected abandoned mines in the upper Animas River 

basin, Colorado, in Nimick, D.A., and von Guerard, P.B., 

eds., Science for watershed decisions on abandoned mine 

lands—Review of preliminary results, Denver, Colorado, 

February 4–5, 1998: U.S. Geological Survey Open–File 

Report 98–0297, p. 47.

APPENDIX

Appendix—Supplemental Information 25

Appendix—Supplemental Information

Laboratory Analytical Methods

Tracer-constituent concentrations were determined in the 

USGS Durango Field Office laboratory. Analytical instrumentation used for these analyses included: Perkin-Elmer 306 

atomic absorption (AA) spectrometer for dissolved-lithium, 

dissolved-potassium, and dissolved-sodium concentrations; 

Kontron SFM25 fluorometer for optical brightener dye 

concentrations; and Beckman φ-210 millivolt meter with 

ion-selective electrodes for bromide and chloride concentrations. Calibration standards were made in the laboratory, 

and reagents for the standards were weighed using a Mettler 

AT100 analytical balance. USGS Standard Reference Water 

(SRW) samples were analyzed for quality assurance; however, 

there are no standard reference water samples for fluorescence.

Instrument Calibrations

Dissolved-lithium concentrations were determined by 

atomic absorption spectroscopy (AAS). Standards were made 

up using the same lithium bromide compound used for the 

field tracer-injection studies. The lithium-specific hollow 

cathode lamp (HCL) was placed in the lamp holder in the 

AA, lamp energy set to 20 milliamps (mA), wavelength set to 

700 nanometers (nm), slit width adjusted to 0.2 nm, and the 

AA turned on and allowed to warm up for about 30 minutes. 

The air-acetylene burner element was lit, the sample inlet 

tube placed in the 0-μg/L sample, and the instrument zeroed. 

The sample inlet tube was placed in the 10-μg/L as lithium 

standard, and the absorbance units displayed on the instrument were entered into a computer spreadsheet. Similarly, the 

25- and 50-μg/L as lithium standards were analyzed and the 

absorbance units entered into the spreadsheet. A linear regression equation was developed by the spreadsheet program, 

and the equation was used to calculate the subsequent lithium 

concentrations of field samples. The detection limit for lithium 

was about 5 μg/L. Every 10 samples, the 0-, 10-, 25-, and 

50-μg/L standards were analyzed, and another regression 

equation was developed for calculation of the lithium concentrations of field samples. Results of lithium calibrations 

are shown in figure A1. Every 10 samples, the USGS T143 

(trace element) Standard Reference Water sample (SRW) was 

analyzed and the accuracy of the determination was checked 

using the SRW result. The field samples were analyzed in 

triplicate; each absorbance reading was an average of absorbance readings over a 10-second interval; therefore, for three 

readings, there were 30 seconds of sample analysis time. The 

final absorbance reading was an average of the three readings. 

Residual standard deviation (RSD, expressed as a percentage) 

was calculated by the standard deviation of the three readings divided by the mean of the three readings (Taylor, 1987); 

RSD’s of lithium determinations ranged from 0.2 to 

7 percent. The range of uncertainty of each lithium determination was expressed as plus and minus the RSD multiplied 

by the concentration. 

Dye concentrations were determined by fluorometry. Dye 

standards were made in the laboratory by weighing Tinopal 

CBS-X optical brightener, the excitation wavelength was set at 

355 nm and emission wavelength set at 430 nm, and a calibration curve was developed. Figure A1 shows the calibration 

curve for relative fluorescence related to dye concentration. 

The field samples were analyzed in triplicate; however, the 

readings were all the same for the triplicate analyses, indicating the sensitivity and accuracy of fluorometry. Hence, the 

RSD’s were zero percent and range of uncertainty was not 

shown on the results for dye concentrations. The detection 

limit for dye concentrations was 0.0 mg/L, or 0.000 relative 

fluorescence units. Water samples were collected by hand at 

the North Star Mine entrance during and after dye injection, 

and the samples were qualitatively analyzed using a handheld ultraviolet (UV) light to observe increased fluorescence 

compared to baseline samples. Unbleached cotton traps can 

typically be used as a qualitative indicator of the presence 

of optical brightener in water that comes in contact with the 

unbleached cotton. Cotton traps were placed in water at all of 

the sites in the North Star area; however, it was realized that 

ferric iron oxyhydroxides from mine drainage rapidly made 

the cotton traps useless as a qualitative detector for the presence of optical brightener.

Dissolved-sodium concentrations were determined by 

AAS. Standards were made using the same sodium chloride 

compound used for the field tracer-injection studies. The 

sodium-specific HCL was placed in the lamp holder in the 

AA, lamp energy set to 10 mA, wavelength set to 589 nm, slit 

width adjusted to 0.6 nm, and the AA turned on and allowed 

to warm up for about 30 minutes. The air-acetylene burner 

element was lit, the sample inlet tube placed in the 0-mg/L 

sample, and the instrument zeroed. The sample inlet tube was 

placed in the 2-mg/L as sodium standard, and the absorbance 

units displayed on the instrument were entered into a computer spreadsheet. Similarly, the 4- and 8-mg/L as sodium 

standards were analyzed and the absorbance units entered 

into the spreadsheet. A linear regression equation was developed by the spreadsheet program, and the equation was used 

to calculate the subsequent sodium concentrations of field 

samples. The detection limit for sodium concentrations was 

about 0.1 mg/L. Every 10 samples, the 0-, 2-, 4-, and 8-mg/L 

standards were analyzed, and another regression equation was 

developed for calculation of the sodium concentrations of field 

samples. Results of sodium calibrations are shown in figure 

A1. Every 10 samples, the USGS M134 (major element) SRW 

sample was analyzed and the accuracy of the determination 

was checked using the SRW result. The field samples were 

analyzed in triplicate; each absorbance reading was an average 

of absorbance readings over a 2-second interval; therefore, 

for three readings, there were 6 seconds of sample analysis 

time. The final absorbance reading was an average of the three 
26 Appendix—Supplemental Information

Figure A1. Graphs showing calibration curves for determination of dissolved lithium and dissolved sodium 

by atomic absorption spectroscopy and optical brightener dye by fluorometry.

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Appendix—Supplemental Information 27

readings. Residual standard deviation (RSD, expressed as a 

percentage) was calculated by the standard deviation of the 

three readings divided by the mean of the three readings (Taylor, 1987); RSD’s of sodium determinations ranged from 0 to 

2.7 percent. The range of uncertainty of each sodium determination was expressed as plus and minus the RSD multiplied by 

the concentration. 

Dissolved-potassium concentrations were determined by 

AAS. Standards were made using the same potassium chloride compound used for the field tracer-injection studies. The 

potassium-specific HCL was placed in the lamp holder in the 

AA, lamp energy set to 12 mA, wavelength set to 

766.5 nm, slit width adjusted to 0.2 nm, and the AA turned on 

and allowed to warm up for about 30 minutes. The air-acetylene burner element was lit, the sample inlet tube placed in the 

0-mg/L sample, and the instrument zeroed. The sample inlet 

tube was placed in the 1-mg/L as potassium standard, and the 

absorbance units displayed on the instrument were entered into 

a computer spreadsheet. Similarly, the 2-mg/L as potassium

standard was analyzed and the absorbance units entered into 

the spreadsheet. A linear regression equation was developed 

by the spreadsheet program, and the equation was used to 

calculate the subsequent potassium concentrations of field 

samples. The detection limit for potassium concentrations 

was about 0.1 mg/L. Results of potassium calibrations are 

shown in figure A2. The USGS M134 (major element) SRW 

sample was analyzed and the accuracy of the determination 

was checked using the SRW result. The field samples were 

analyzed in triplicate; each absorbance reading was an average 

of absorbance readings over a 2-second interval; therefore, 

for three readings, there were 6 seconds of sample analysis 

time. The final absorbance reading was an average of the three 

readings. Residual standard deviation (RSD, expressed as a 

percentage) was calculated by the standard deviation of the 

three readings divided by the mean of the three readings 

(Taylor, 1987); RSD’s of potassium determinations ranged 

from 1 to 4.5 percent. 

Dissolved-bromide and dissolved-chloride concentrations 

were determined using a millivolt meter and ion-selective 

electrodes. Standards were made in the laboratory by weighing the same salts used in the field tracer studies. Millivolt 

(mV) readings corresponding to the standards were entered 

into a spreadsheet program, and a polynomial equation was 

developed for the nonlinear relation between millivolts and 

concentration. Figure A2 shows the relations between millivolts, bromide concentration, and chloride concentration. The 

range of uncertainty for bromide and chloride concentrations 

were determined by the maximum error observed on repeated 

measurements of selected samples; the range of measurements 

were entered into the polynomial equation to represent the 

range of uncertainty for bromide and chloride concentrations. 

The USGS M140 SRW was analyzed for chloride; however, 

there was not a bromide analysis for this SRW.

Quality Assurance

Since 1962, the USGS has operated the Standard Reference Sample Project (SRSP) to evaluate the performance of 

USGS, cooperator, and contractor analytical laboratories that 

analyze chemical constituents of environmental samples. The 

laboratories are evaluated by using performance-evaluation 

samples, which are called Standard Reference Water (SRW) 

samples (Long and others, 1998). The SRW samples also are 

available to USGS field offices and research laboratories. 

For the purposes of this study, the USGS SRW samples were 

analyzed for quality assurance of the laboratory analyses 

determined in the USGS Durango Field Laboratory. In addition to the SRW, accurate and precise analytical determinations were assured by recalibrating the AA every 10 samples, 

by averaging the AA readings over many seconds of burn 

time, and by repeated measurements using the ion-selective 

electrodes, AAS, and fluorometry. Ranges of uncertainty were 

calculated for each individual determination by AAS method, 

and the maximum errors were calculated for concentrations 

by ion-selective electrode. A comparison of the SRW values 

to concentrations determined as part of this study are shown 

in table A1. The uncertainty ranged from 0.5 to 12.9 percent 

for AAS methods, and the uncertainty was about 13.6 percent 

for the ion-selective electrode. The SRW samples available at 

the time of this study (M134, M138, and M140) did not have 

a bromide analysis; therefore, there is no SRW comparison for 

bromide. In addition, there are no SRW samples for fluorometric methods.

Water-quality data collected by the USGS are available on the National Water Information System (NWIS), and 

the water-quality data are accessible to the public through 

the USGS Web site http://water.usgs.gov/nwis. However, 

the analytical determinations presented in this report do not 

represent ambient water-quality conditions because the tracer 

constituents were injected into the alpine stream. Therefore, 

the analytical data in this report are not available from the 

USGS NWIS.
28 Appendix—Supplemental Information

Figure A2. Graphs showing calibration curves for determination of dissolved potassium by atomic absorption 

spectroscopy and dissolved bromide and dissolved chloride by ion-selective electrode.

POTASSIUM CALIBRATION

Potassium = 166Abs

R2 = 1.0

0.5

1.0

1.5

2.0

2.5

0

0

0.002 0.004 0.006 0.008 0.01 0.012 0.014

ABSORBANCE

POTASSIUM STANDARD 

CONCENTRATION, IN

MILLIGRAMS PER LITER

BROMIDE CALIBRATION

Bromide = 0.00012(mV)2 - 0.025mV + 1.28

R 2 = 0.98

0

0.1

0.2

0.3

0.4

0.5

0.6

0 20 40 60 80 100 120

MILLIVOLTS (mV)

BROMIDE STANDARD 

CONCENTRATION, IN

MILLIGRAMS PER LITER

CHLORIDE CALIBRATION

Chloride = 0.0036(mV)2 - 1.15mV + 92.2

R2 = 0.99

0

2

4

6

8

10

12

14

100 110 120 130 140 150 160

MILLIVOLTS (mV)

CHLORIDE STANDARD 

CONCENTRATION, IN

MILLIGRAMS PER LITER
Appendix—Supplemental Information 29

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